I have never had any issues with power washing a dirty engine bay, just make sure all of the caps are on tight and don't spray directly into the air intake box.
workng at a dealership has shown me how bad people let their cars go...i'm a smoker...but would never let my car smell like some of the ashtrays that come in..let alone dog hair, 30lbs of smoke packs,coffee cups and fast food bags. there is times where i hold my breath just to move a car from the drivethru to outside to keep myself from puking
it doesn't take much to keep it clean if your car was clean and waxed before the rain then it will be clean after the rain
I get my car washed every weekend, and wash it every few days when warm! usually wax it every month!